Me and my friends have been playing 8th edition for just over a year now and I have learnt a lot, I’ve also read and re-read rules to try and understand what they actually mean because there’s is a lot of “1d4chan says this” going on (which turns out to be wrong). Cannons are a particularly sore subject for me and as such I treat them with the utmost scrutiny. I have interpreted the rules for cannons like this:

After reading through the rules, while carnosaurs may be large targets, a player with a cannon will never aim at the carnosaur. They aim 10” from the back of the base almost every time. Where ever that spot on the battlefield may be, that is their target, not the carnosaur itself and so the large target rule does not come into effect (yet). This means that walls, monstrous creatures, buildings etc will stop a cannon ball before it comes into contact with the carnosaur, and infantry units (friend and foe) May block line of sight depending. So in theory you can hide a carnosaur behind a wall.

My opponent may circumnavigate this by aiming at my carnosaur thus making the place they are aiming beyond the wall/obstacle but risk over shooting if they roll more than a 2 on the artillery dice.

Am I interpreting that correctly?

Another thing - rules for shooting state that ranged weapons can only shoot at what they can see if their front arc. The BRB states that a war machine may pivot towards their target in the shooting phase (changing from movement phase as per FAQ). Does this mean that if I am outside of a cannons front arc in the shooting phase I am not a viable target? My opponent would had to of pivoted in the movement phase In order to make the flankers a viable target? I understand this makes little difference in reality but will make my opponent think more rather than just treating cannons as a 360 degree auto-turret for monsters.